1. Field of the invention
The present invention concerns device for rapidly switching or changing-over a luminous beam, in particular when this luminous beam carries coded data. One of the specific applications of the invention concerns optical or light switching between optic fibers.
2. Description of the prior art
Among the dispositions of the prior art can be cited structures in which the space deflection of an optical beam is carried out by mirrors constituted by semi-reflecting layers that introduce losses which are not negligible (hardly lower than a square centimeter). Devices are also known where the deflection of luminous beams is introduced by the total reflection of the light in electro-optical crystals. The drawback of these devices resides in the crystal itself, in general lithium niobate which, for reasons of purity, is only available in small dimensions which implies that the pitch of the electrodes that it bears and which act to apply thereto an electric control field is very small. Consequently, electro-optical crystal devices optical systems. Furthermore, the crystal reacts only slightly to the electric field, which implies use of high control voltages.
With the aim of overcoming these problems, the applicant filed on July 4. 1983 a French patent application under No. 83 11074 and entitled: "Dispositif de commutation optique a deplacement de fluide et dispositif de composition d'une ligne de points" no French Pat. No. 2,548,795. This invention proposed to use electrically controlled movements of very small volumes of liquid without the intervention of moving mechanical elements, in order to modify locally the refraction conditions encountered by the luminous beams that are propagated in the device. These refraction modifications allow to shift the paths of the luminous beams and thus to realize a change-over between the various propagation paths, especially between the optic fibers. It is therefore possible to realize change-over devices comprising electrically controlled means of liquid displacement that allow causing very small volumes of this liquid in the form of layers or globules to flow from one zone to another under the action of electrically generated moving power due to the local variations of electrical fields due to the stepwise voltage application on the control electrodes. The distance between the electric field application electrodes can be, in this utilization, in the range of tens of micrometers. To facilitate the practical realization and so as not to excessively "diaphragm" the luminous beams, it is advantageous to provide electrodes that are transparent to the luminous radiance involved, it is possible to use, for example, electrodes made of mixed indium and tin oxide (ITO electrodes) disposed on glass and engraved by microlithography. The drawback of this solution is the introduction of supplementary interfaces, typically, between glass and transparent electrode and between transparent electrode and confined fluids (gas or liquid), as well as the introduction of a layer (transparent electrode) generally more refractive than its carrier or support and the confined fluid. The disparity in refraction indice of the mediums crossed by the luminous rays brings about the existence of interference reflections that are prejudicial to the detection of signals levels.